Tower solar thermal power technique is among the best solar thermal power techniques for constructing large-scale, industrialized power plants taking account of both technical and economic factors. Among tower thermal power techniques, those using Brayton cycle outperform those using Rankine cycle in aspects such as high efficiency, shorter working process, less water consumption, and easy to implement solar energy and fossil (oil or gas) hybrid power generation. The tower Brayton thermal power techniques are more promising than those industrialized tower Rankine techniques. German National Space Agency Solar R & D Center (DLR) and Isreal Weizmann Institute of Science (WIS) are outstanding representative developers of tower Brayton solar thermal power techniques.
A Brayton cycle-based tower power generator uses a turbine to drive the generator, and uses compressed-air which is heated by solar energy to a temperature of about 900° C. as the working fluid (working fluid with a temperature lower than 900° C. may remarkably decrease the efficiency of the turbine). A volumetric receiver developed by DLR and WIS uses a quartz glass cover which can allow the sunshine to pass while maintaining the air pressure within the cover. A sealed interface between the quartz glass cover and the body of the volumetric receiver may also require water cooling to ensure the reliability of the sealing under high temperature. In order to prevent recrystallization of the quartz glass to become opaque at a temperature above 1000° C., it is necessary to use high purity quartz glass. Compression-resistant high purity quartz glass covers are hard to manufacture, expensive, and hard to be produced in large size, which restricts the maximum power capacity of a single tower Brayton thermal solar power unit to be within 200 KW (a completed experimental unit has a capacity of only 100 KW). There have been cases in longer-term operation where such volumetric receivers have the quartz glass or the sealing damaged, and this has become the bottleneck in technological development. In addition, in conventional tower solar thermal power techniques, molten salt is generally used as the heat storage agent, and the most commonly used salt is a mixture of potassium nitrate and sodium nitrate. Since high-temperature air is required, the molten salt cannot be used in a tower Brayton solar thermal power plant because the upper limit of working temperature of molten salt is 600° C., much lower than 900° C. which is the temperature required by the turbine for optimal operation efficiency. Thus, the use of molten salt will make the operation efficiency of a tower Brayton thermal power unit with heat storage so low that the apparatus cannot be put to use.